Electronic Spectroscopies by a Novel STM with functional Semiconductor Tips

为了寻找合适的半导体材料作为STM针尖，我们通过激光辐照下的STM/STS测量和带有导电针尖的AEM测量静电力来表征n-GaAs表面自组装InAs点覆盖表面的近表面电学特性。结果表明，在InAs点结构附近检测到较小的光响应信号，而在周围的润湿层区域检测到较大的光响应信号。此外，时间分辨隧道电流测量表明，这种光响应信号主要来自于光激发载流子引起的表面耗尽的减少。这些结果表明，InAs点附近的表面耗尽被抑制，这与体InAs表面聚集电子的地方非常相似。我们用带有导电针尖的AEM测量了工作在AFM针尖和样品之间的静电力。通过在与外加交流偏置频率相同的两个频率和两个频率的倍频上的锁定检测技术，成功地估计了表面损耗程度。此外，得到的静电力数据清楚地表明，InAs点附近的表面耗尽被抑制，这与STM/STS的结果是一致的。因此，InAs覆盖的GaAs是一种很有前途的半导体针尖材料，因为它的表面耗尽被抑制了。

In order to find the proper semiconductor materials for STM tips, we have characterized the near surface electrical properties of self-assembled InAs dot-covered surfaces on n-GaAs through both the STM/STS measurements under the laser irradiation and the electrostatic force measurements by AEM with a conductive tip.We characterized the near surface electrical properties of The self-assembled InAs dot-covered surfaces on n-GaAs through the STM/STS measurements under the laser irradiation. As a result, the small photo-response signal was detected near the InAs dot structures, while the large signal was detected from the surrounding wetting layer region. In addition, the time-resolved tunneling current measurements revealed that such photo-response signal mainly came from the reduction of the surface depletion due to the photo-excited carries. These results indicates that the surface depletion is suppressed near the InAs dots, which is very similar as the bulk InAs surface where the electrons are accumulated.We measured the electrostatic force, which is working between the AFM tip and the sample, on the similar sample as above by the AEM with a conductive tip. Through the lock-in detection technique at the two frequencies which are the same and the double frequencies as applied AC bias frequency, we succeeded in estimating the degree of surface depletion. Moreover, the obtained electrostatic force data clearly indicated that the surface depletion is suppressed near the InAs dots, which is consistent with the STM/STS results.As a result, InAs covered-GaAs is one of the promising materials for the semiconductor tip because the surface depletion is suppressed on its surface.